DE4333837B4 - 4-fluorobenzenes and their use in liquid-crystal mixtures - Google Patents

Abstract

worin R Methyl, Ethyl, Propyl, Butyl, Pentyl, Hexyl, Heptyl, Octyl, Nonyl und Decyl bedeutet.4-fluorobenzene derivatives of the formula (I) and (II)

wherein R is methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl.

Description

The unusual Combination of anisotropic and fluid behavior of liquid crystals has for their use in electro-optical switching and display devices guided. It can their electrical, magnetic, elastic and / or their thermal Properties for orientation changes be used. Optical effects can be, for example, with Help of birefringence, the incorporation of dichroic dye molecules (guest host mode) or the light scattering.

The Practice requirements are constantly increasing not least because of the ever increasing number of light valve types (TN, STN, DSTN, TFT, ECB, DECB, DS, GH, PDLC, NCAP, SSFLC, DHF, SBF etc.). In addition to thermodynamic and electro-optical parameters, such as Phase sequence and phase temperature range, refractive index, birefringence and dielectric anisotropy, switching time, threshold voltage, transconductance of electro-optical characteristic, elastic constants, electrical Resistance, multiplexability or pitch and / or polarization in chiral phases, the stability of liquid crystals to moisture, Gases, temperature and electromagnetic radiation, as well as against the Materials with which they are used during and after the manufacturing process in Compounds (e.g., alignment layers) are of great importance. Of the toxicological and ecological Unbiasliness as well as price are becoming increasingly important to.

A broad overview of the field of liquid crystals can be found, for example, in the following references and the references contained therein:
H. Kelke, H. Hatz: Handbook of Liquid Crystals, Verlag Chemie, Weinheim 1980 WE De Jeu: Physical Properties of Liquid Crystal Materials, Gordon and Breach, 1980; H. Cress: Dielectric Behavior of Liquid Crystals, Advances in Physics, Berlin 30 (1982) 10, 507-582.
B. Bahadur: Liquid Crystals: Applications and Uses, World Scientific, 1990.
Landolt-Börnstein, New Series, Group IV, Volume 7 Liquid Crystals, 1992-1993.

There Individual connections so far not all the above requirements at the same time can exist Ongoing demand for new improved liquid crystal mixtures and thus on a variety of mesogenic and non-mesogenic compounds different structure, an adaptation of the mixtures enable a wide variety of applications.

Of the Use of special derivatives of 4-fluorobenzene in nematic liquid crystal mixtures has been for a while (see: EP-A 0 494 368, WO 92/06 148, EP-A 0 460 436, US Pat. DE-A 4 111 766, DE-A 4 112 024, DE-A 4 112 001, DE-A 4 100 288, DE-A 4,101,468, EP-A 0 423 520, DE-A 3 923 064, EP-A 0 406 468, EP-A 0 393 577, EP-A 0 393 490, EP-A 0 316 186, DE-A 32 33 641).

worin R Methyl, Ethyl, Propyl, Butyl, Pentyl, Hexyl, Heptyl, Octyl, Nonyl und Decyl bedeutet.The present invention relates to novel 4-fluorobenzene derivatives of the formula (I) and (II)

wherein R is methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl.

The substances according to the invention show especially broad nematic phases, high clearing points and low melting points.

The Preparation of the compounds of the invention can by literature known and familiar to those skilled methods respectively.

Starting from 4-fluorophenol, compounds of the formula (I) are obtained by etherification Trans-4-alkylcyclohexylmethanols and trans-4-alkylcyclohexylmethyl halides (Scheme 1).

The Esterification of 4-fluorophenol with 4- (trans-4-alkylcyclohexyl) benzoic acid or 4- (Trans-4-alkylcyclohexyl) benzoic acid halides provide the Compounds of the formula II (Scheme 2).

• – Tetrahedron 36 (1980) 2409,
• – Organic Synthesis, Coll. Vol. 5 (1973) 258,
• – Journal of the American Chemical Society 69 (1947) 2451,
• – Synthesis (1981) 1.

Schema 1:

X = OH, Cl, Br Schema 2:

X = OH, ClTo carry out the syntheses, see, for example:

• Tetrahedron 36 (1980) 2409,
• - Organic Synthesis, Coll. Vol. 5 (1973) 258,
• - Journal of the American Chemical Society 69 (1947) 2451,
• Synthesis (1981) 1.

Scheme 1:

X = OH, Cl, Br Scheme 2:

X = OH, Cl

liquid crystalline Compounds of the formula (I) and / or (II) can be prepared use of nematic or even chiral nematic liquid-crystal mixtures, the for the application in electro-optical or fully optical elements, e.g. Display elements, switching elements, light modulators, elements for Image processing, signal processing or generally in the field of nonlinear optics are suitable.

object The invention also relates to liquid-crystal mixtures, the one or more compounds of the formula (I) and / or (II) contain.

The liquid-crystal mixtures according to the invention generally consist of 2 to 20, preferably 2 to 15 components, including at least one, preferably 1 to 5, particularly preferably 1 to 3, compounds of the formula (I) and / or (II). The LC mixtures according to the invention can be, for example, nematic or chirally nematic. Further constituents of the mixtures according to the invention are preferably selected from the known compounds having nematic or cholesteric phases; These include, for example, biphenyls, terphenyls, phenylcyclohexanes, bicyclohexanes, cyclohexylbiphenyls, mono-, di- and trifluorophenyls. In general, the commercially available liquid crystal mixtures are be even before the addition of the compound (s) according to the invention as mixtures of various components, of which at least one is mesogenic.

• – 4-Fluorbenzole, wie beispielsweise in EP-A 494 368, WO 92/06 148, EP-A 460 436, DE-A 4 111 766, DE-A 4 112 024, DE-A 4 112 001, DE-A 4 100 288, DE-A 4 101 468, EP-A 423 520, DE-A 392 3064, EP-A 406 468, EP-A 393 577, EP-A 393 490 beschrieben,
• – 3,4-Difluorbenzole, wie beispielsweise in DE-A 4 108 448, EP-A 507 094 und EP-A 502 407 beschrieben,
• – 3,4,5-Trifluorbenzole, wie beispielsweise in DE-A 4 108 448, EP-A 387 032 beschrieben,
• – 4-Benzotrifluoride, wie beispielsweise in DE-A 4 108 448 beschrieben,
• – Phenylcyclohexane, wie beispielsweise in DE-A 4 108 448 beschrieben.

Suitable further constituents of nematic or chirally nematic liquid-crystal mixtures according to the invention are, for example

• 4-fluorobenzenes, as described, for example, in EP-A 494 368, WO 92/06 148, EP-A 460 436, DE-A 4 111 766, DE-A 4 112 024, DE-A 4 112 001, DE-A 4,100,288, DE-A 4,101,468, EP-A 423 520, DE-A 392 3064, EP-A 406 468, EP-A 393 577, EP-A 393 490,
• 3,4-difluorobenzenes, as described, for example, in DE-A 4,108,448, EP-A 507,094 and EP-A 502,407,
• 3,4,5-trifluorobenzenes, as described, for example, in DE-A 4,108,448, EP-A 387,032,
• 4-benzotrifluorides, as described, for example, in DE-A 4,108,448,
• - Phenylcyclohexane, as described for example in DE-A 4,108,448.

From the one or more compounds of the invention of formula (I) and / or (II) contain the liquid crystal mixtures in general 0.1 to 70 mol%, preferably 0.5 to 50 mol%, in particular 1 to 25 mole%.

liquid crystalline Mixtures containing compounds of general formula (I) and / or (II) are particularly for the use in electro-optical switching and display devices (Displays) suitable. Switching and display devices (LC displays) generally have u.a. following components: a liquid crystalline Medium, carrier plates (e.g., glass or plastic) coated with electrodes from which at least one is transparent, at least one orientation layer, Spacers, adhesive frames, polarizers and color displays thin color filter layers.

Further possible Components are antireflective, passivation, leveling and barrier layers and electrically non-linear elements, such as thin-film transistors (TFT) and metal-insulator-metal (MIM) elements. In detail is the structure of liquid crystal displays already in relevant Monographs (e.g., E. Kaneko, "Liquid Crystal Television Displays: Principles and Applications of Liquid Crystal Displays ", KTK Scientific Publishers, 1987, pages 12-30 and 63-172).

to physical characterization of the compounds of the invention become different measuring methods used.

The phase transition temperatures are determined during heating using a polarizing microscope based on the texture changes. The determination of the melting point, however, is carried out with a DSC device. The indication of the phase transition temperatures between the phases isotropic (I) nematic (N or N *) Smectic-C (S _C or S _C *) Smectic-A (S _A or S _A *) crystalline (X) Glass transition (Tg) takes place in ° C, and the values stand between the phase designations in the phase sequence.

electro-optical Investigations are carried out by methods known from the literature (for example B. Bahadur: Liquid Crystals Application and Uses, World Scientific, 1990, vol.I).

For nematic liquid Crystals (pure or in mixture) are the values for the optical and dielectric Anisotropy and the electro-optical characteristic at a temperature from 20 ° C added.

liquid crystals at 20 ° C have no nematic phase are added to 10 wt .-% in ZLI-1565 (commercial nematic liquid-crystal mixture the company E. Merck, Darmstadt) and the values from the results extrapolated to the mixture.

Electro-optical characteristics are determined by the transmission of a measuring cell. For this purpose, the cell is positioned between crossed polarizers in front of a light source. Behind the cell is a Light detector whose sensitivity is optimized by filters on the visible region of the light. Analogous to the stepwise increase of the voltage applied to the cell, the change of the transmission is recorded. Parameters such as threshold voltage and slope are determined from this.

The optical anisotropy is measured with an Abbé refractometer (Zeiss) certainly. For orientation of the liquid crystal is on the Prisma an orientation layer obtained from a 1 wt .-% Lecithin-methanol solution, applied.

to Determination of the dielectric anisotropy are each a measuring cell with homeotropic and planar orientation and their capacities and Dielectric Losses with a Multi Frequency LCR Meter (Hewlett Packard 427417). The dielectric constants are calculated as described in the literature (W. Maier, G. Meier: Z. Naturforsch., 16a, 1961, 262 and W.H. de Jeu, F. Leenhonts: J. Physique 39, 1978, 869),

The electrical size HR (Holding & Ratio) will be appropriate the literature references (M. Schadt, Linear and nonlinear liquid Crystal Materials, Liquid Crystals, 1993, Vol.14, No. I, 73-104).

to Determination of τ and K becomes the measuring cell on the turntable of a polarizing microscope between crossed Analyzer and polarizer attached. For the determination of the contrast (K) becomes the measuring cell positioned by turning so that a photodiode minimum Light passage indicates (dark state). The microscope illumination is regulated so that the Photodiode for all cells display the same light intensity. After a switching operation changes the light intensity (Bright state) and the contrast is from the ratio of the light intensity of this conditions calculated.

example 1

4-fluorophenyl (trans-4-pentylcyclohexyl) methyl ether

Phasenfolge: X 22 l 1 N0 X1.97 g (7.50 mmol) of triphenylphosphine are mixed at 0 ° C in 30 ml of tetrahydrofuran with 1.31 g (7.5 mmol) of diethyl azodicarboxylate and stirred for 0.5 h at room temperature. Thereafter, 0.84 g (7.50 mmol) of 4-fluorophenol and 0.92 g (5.00 mmol) of trans-4-pentylcyclohexylmethanol are added and the mixture is stirred at room temperature for 18 h. After evaporation of the solvent and chromatography on silica gel with hexane 0.79 g of product are obtained.

Phase sequence: X 22 l 1 N0 X

Beispiel 3 4-Fluorphenyl-(tans-4-butylcyclohexyl)methylether

Beispiel 4 4-Fluorphenyl-(trans-4-hexylcyclohexyl)methylether

Beispiel 5 4-Fluorphenyl-(trans-4-heptylcyclohexyl)methylether

Prepared analogously to Example 1: Example 2 4-fluorophenyl (trans-4-propylcyclohexyl) methyl ether

Example 3 4-Fluorophenyl- (tans-4-butylcyclohexyl) methyl ether

Example 4 4-Fluorophenyl- (trans-4-hexylcyclohexyl) methyl ether

Example 5 4-Fluorophenyl- (trans-4-heptylcyclohexyl) methyl ether

Example 6

4- (trans-4-pentylcyclohexyl) benzoic acid 4-fluorophenyl ester

Phasenfolge: X 91, 9 N 157,2 I 156,8 N 57,1 X1.03 g (5.00 mmol) of dicyclohexylcarbodiimide, 0.99 g (5.00 mmol) of 4- (trans-4-pentylcyclohexyl) benzoic acid and 0.56 g (5.00 mmol) of 4-fluorophenol are mixed with 10 mg 4-N, N-dimethylaminopyridine in 30 ml of dichloromethane for 6 h at room temperature. After filtration, evaporation of the solvent and chromatographic purification (silica gel / hexane) 1.27 g of product are obtained.

Phase sequence: X 91, 9 N 157.2 I 156.8 N 57.1 X

Beispiel 8 4-(Trans-4-butylcyclohexyl)benzoesäure-4-fluorphenylester

Beispiel 9 4-(Trans-4-hexylcyclohexyl)benzoesäure-4-fluorphenylester

Beispiel 10 4-(Trans-4-heptylcyclohexyl)benzoesäure-4-fluorphenylester

The following are produced analogously to Example 6: Example 7 4- (Trans-4-propylcyclohexyl) benzoic acid 4-fluorophenyl ester

Example 8 4- (Trans-4-butylcyclohexyl) benzoic acid 4-fluorophenyl ester

Example 9 4- (Trans-4-hexylcyclohexyl) benzoic acid 4-fluorophenyl ester

Example 10 4- (Trans-4-heptylcyclohexyl) benzoic acid 4-fluorophenyl ester

applications

In of Table 1 are the substances of Example 1 and Example 6 (S1 and S6) with known substances (R1, R2) listed. It shows that S6 the highest clearing point when cooling the lowest crystallization point and the lowest during heating Melting point. When adding 10% by weight of the substances to a commercial one available nematic liquid crystal mixture (ZLI 1565, E. Merck, Darmstadt), it is found that S6 has a higher clearing point as R1 and R2 in ZLI 1565 induced.

The substance S1, with its mesogenic core with only two ring systems, has lower LC phases, but also lowers the glass transition, so that a lower viscosity and a lower temperature dependence of the viscosity in the working temperature range can be expected. Furthermore, the value of the birefringence is favorably changed, eg compared to R1 at a reduced temperature of T / T _NI = 0.840. The low melting point of the substances is favorable for the development of mixtures.

Claims (7)

4-fluorobenzene derivatives of the formula (I) and (II)

wherein R is methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl. Liquid crystal mixture, containing at least one compound of the formula (I) and / or (II) according to claim 1. Liquid crystal mixture, containing at least one compound of the formula (I) and / or (II) according to claim 1 or 2, characterized in that the liquid-crystal mixture is nematic. liquid crystal mixture according to claim 2 or 3, characterized in that it is 0.1 up to 70 mol% of one or more compounds of the formula (I) and / or (II). liquid crystal mixture according to one or more of claims 2 to 4, characterized in that it 2 contains up to 20 components. liquid crystal mixture according to one or more of claims 2 to 5, characterized in that it 1 to 5 compounds of formula (I) and / or (II). Switching and / or display device, including carrier plates, Electrodes, at least one polarizer, at least one orientation layer and a liquid crystalline Medium, characterized in that the liquid-crystalline medium a liquid crystal mixture according to one or both of the claims 2 and 3 is.